Marijuana: Hazy Health Risks

With more than half of Americans now in support of legalizing marijuana (Cannabis sativa)—and nearly half saying they have tried it—we’ve come a long way since smoking pot carried a social stigma, not to mention political liability. Consider Bill Clinton, who in 1992 acknowledged that he had “experimented” with marijuana, but stressed that he didn’t inhale. In contrast, President Obama said he not only “inhaled frequently” when he was young, but “that was the point.”

Since the late 1990s, twenty states, along with the District of Columbia, have legalized medical marijuana. In late 2012, Colorado and Washington became the first states to legalize recreational use—and more states, including Alaska and Oregon, may soon follow as the movement gains momentum. There’s little question that marijuana has certain medical benefits, but do we know enough about its health effects to give a green thumbs up to recreational use?

Marijuana: high hopes for medical use

Four scientific panels, including ones from the National Institutes of Health and the American Medical Association, have concluded that medical marijuana can relieve certain kinds of pain, help control nausea from chemotherapy, improve appetite in people with AIDS and lessen spasticity in multiple sclerosis. Marijuana is also sometimes prescribed for seizures, migraines, insomnia, glaucoma, post-traumatic stress disorder and other conditions. In fact, between 1850 and 1942, marijuana was listed in the U.S. Pharmacopeia as a medicinal drug.

This doesn’t mean it’s good for all that ails you, however. A paper in Arthritis Care & Research in March noted that evidence is lacking to support the use of marijuana in managing rheumatic conditions, such as rheumatoid arthritis and lupus.

The benefits of marijuana are attributed to its cannabinoid compounds, including tetrahydrocannabinol (THC) and cannabidiol (CBD), which mimic natural substances in the brain that are associated with pain sensations, appetite and mood. THC is also the chief psychoactive ingredient.

Most patients smoke the dried plant for the quickest effects; its active ingredients can also be delivered through capsules, vaporizers, mouth sprays, suppositories, liquid extracts, and foods and beverages. With the exception of two THC medications (dronabinol, nabilone) approved by the Food and Drug Administration (FDA), however, dosing is generally unpredictable, since the levels of active ingredients vary among plants, and absorption rates vary among users.

Recreational reality check

Marijuana is often perceived as relatively harmless compared to tobacco, in part because people tend to smoke far fewer marijuana joints than regular cigarettes. But, as accumulating research suggests, even if it’s not as bad, it may still do long-term damage.

Marijuana smoke contains hundreds of chemicals, including many of the same carcinogens found in tobacco smoke, such as nitrosamines, polycyclic aromatic hydrocarbons and acetaldehyde—with some at even higher concentrations. In a UCLA study some years ago, marijuana cigarettes released fives times as much carbon monoxide into the bloodstream as tobacco cigarettes, and three times as much tar into the lungs. Experimental work has also found that marijuana smoke can increase DNA-damaging free radicals. Scientists are thus urging the FDA to investigate marijuana with the same rigor that it does new medications, and that legal use be strictly regulated.

What marijuana research shows

Much is still unknown about the health effects of marijuana, both good and bad, because of the inherent difficulty of doing research, especially human trials, on an illegal substance. Most studies have been done in animals and test tubes. Moreover, observational studies of recreational drug use are problematic because they typically use participants’ self-reports, which are not very reliable. Another research challenge is that marijuana users are likely to also smoke tobacco, drink alcohol, take other drugs and have other habits that set them apart from non-users. Still, here’s what you should know before you light up.

Lung effects. Because it’s an airway irritant, marijuana smoke increases respiratory symptoms, including coughing and wheezing. In some ways, marijuana may be even more detrimental than cigarettes, since pot smokers tend to inhale more deeply and hold the smoke in their lungs longer, plus joints have no filters and the smoke is hotter. A 2007 study in Thorax found that one joint was equivalent to 2.5 to 5 tobacco cigarettes in terms of causing airway obstruction. On the other hand, unlike with cigarettes, there is no evidence that marijuana use alone leads to COPD (chronic obstructive pulmonary disease). In fact, a large study in the Journal of the American Medical Association in 2012 found that moderate use (up to one joint a day for seven years) did not significantly impair lung function—though the authors did caution that heavier users may experience an accelerated decline in pulmonary function. What about lung cancer? The association remains unclear. Lung biopsies of chronic pot smokers have revealed precancerous changes in respiratory cells. And a large Swedish study in Cancer Causes & Control in 2013 linked heavy marijuana use to a more than two-fold increase in lung cancer risk over 40 years. That’s a lesser risk than with tobacco, but some researchers still think it’s prudent to add lung cancer to the list of marijuana’s adverse effects.

Other cancers. As noted in a California Environmental Protection Agency (EPA) report, observational studies have also linked marijuana smoke to increased risk of other cancers, including bladder cancer, with the strongest evidence being for head and neck cancers. In addition to its carcinogenic compounds, marijuana smoke may alter endocrine functioning, which could, for example, increase the risk of ovarian, breast, uterine and testicular cancer. Marijuana’s potential adverse effects on the immune system might further increase cancer risk. Complicating matters, however, some studies have not only failed to find associations between marijuana and cancer, but at least one linked long-term moderate use to a reduced risk of head and neck cancers. Cannabinoids in marijuana have anti-inflammatory and anti-tumor effects, the authors said.

Cardiovascular effects. Marijuana increases heart rate and may increase inflammation in blood vessels. There are reports of increased heart attacks and cardiomyopathy (deterioration of the heart muscle) in marijuana smokers, as well as increased angina. A paper in the International Journal of Clinical Practice in 2009 concluded that marijuana smoking likely increases the risk of atrial fibrillation (a type of abnormal heart rhythm) and that large doses lead to a drop in blood pressure when standing, which could result in dizziness and falls. Some preliminary research suggests it may also increase strokes. On the other hand, lab studies have shown that cannabinoids have neuroprotective effects, which some researchers think may help limit brain damage after a stroke.

Mental effects. Marijuana decreases concentration and short-term memory, slows reaction time and causes drowsiness and lethargy. It increases anxiety and panic attacks in some people, instead of providing a “high.” Chronic use can lead to dependence and possible long- term memory problems. Some studies have linked marijuana to mental disorders, including depression and psychosis, though that doesn’t mean the drug is the cause; it may be that people with such problems are more likely to use marijuana.

Bottom line: An upshot of marijuana legalization is that this should open the door for more research, which is needed to determine the best doses and delivery systems for medical use as well as the benefit-to-risk ratio for all users. In the meantime, we think medical marijuana is a reasonable option for many people—when prescribed by a doctor and taken via a nonsmoking route.

As for recreational use, we don’t endorse the smoking of any substance. No smoke is good smoke. Still, throughout history, humans have sought ways to relax—and marijuana is less risky than cigarettes and other drugs when used occasionally and at low doses.

People with certain medical conditions, including cardiovascular disease, should use marijuana with caution, if at all, however. Pregnant and breastfeeding women, teenagers (whose brains are more vulnerable) and anyone with a history of mental illness should avoid it. And, of course, no one should smoke and drive (see box).

Like alcohol, marijuana impairs driving performance. The question is how much. Advocacy groups claim that marijuana affects psychomotor skills only mildly and that this doesn’t seem to play a significant role in road accidents compared to alcohol.